The research, published in Body Image, examined how a fitness professional’s perceptions of a hypothetical client’s motivation to exercise, as well as the weight status of the client, jointly affected the instructors’ motivation to train a client.

Lead author John Curtin Distinguished Professor Nikos Ntoumanis, from the School of Psychology at Curtin University, said an individual’s body weight can have a profound impact on other people’s perceptions of and behaviour towards them.

“We know from past research that people who are overweight and obese report experiencing weight-based discrimination, stigmatisation and unjust treatments across various sectors, including the exercise industry,” Professor Ntoumanis said.

“This study explored whether a fitness professional’s motivation to instruct a hypothetical new client, their style of communication with the client, and beliefs about the client’s ability to overcome barriers to exercise were influenced by both the instructors’ perceptions of the client’s motivation and the clients’ weight.

“Our findings suggest that perceptions of a client’s motivation and the client’s body weight can independently influence fitness professionals’ motivation to instruct, interactions with and beliefs about their clients. In a nutshell, fitness instructors were more motivated to train people with a normal weight than those who were overweight. It also shows fitness instructors were more motivated to train people who were motivated for internal reasons, such as the importance of exercise, as opposed to external reasons, including pressure from others.”

Professor Ntoumanis said future research should examine how weight-stigmatising attitudes and interactions within the exercise sector could potentially negatively affect the quality of the service fitness instructors provided, and subsequently impact the overweight clients’ commitment to exercise and their quality of life.

“While instructors are responsible for helping clients make positive, long-lasting changes to their lifestyles, they are – like everyone – exposed to western cultural biases about obesity and associated weight stigma,” Professor Ntoumanis said.

“It is therefore imperative that fitness professionals are made aware of the potential positive or negative impact their preconceived ideas about their clients, based on clients’ weight and perceived motivation to exercise, have.”

Professor Ntoumanis said preliminary research findings from other studies indicated brief educational films targeting weight bias and additional motivation training for fitness professionals could help improve the quality of service and a client’s motivation to remain committed to exercise.